1. Field of the Invention
The present invention relates to an oil application apparatus which is one of constituent parts of a fixing apparatus in an electrostatic copying machine, an electrophotographic printer, or the like.
2. Description of the Related Art
In a fixing apparatus in an electrostatic copying machine, an electrophotographic printer, or the like, there was a possibility that toner transferred onto a sheet of recording paper was deposited on a heat-fixing roll when the toner was fixed. To prevent the next sheet of recording paper from being contaminated with the toner, a small amount of release oil such as silicone oil was applied onto the fixing roll by an oil application roller so that the toner was prevented from being deposited on the heat-fixing roll, and the recording paper was prevented from being curled up by sticking to the heat-fixing roll. Various application rollers having such a function have been already proposed. For example, there is known an oil application roller using a perforated hollow pipe of metal or a cylindrical molded product of heat-resisting fiber as an oil-holding member for storing release oil to be applied. The known oil application roller has an oil migration layer of heat-resisting felt provided on a surface of the cylindrical molded product, and an oil application amount control layer of a porous film further provided on the oil migration layer. Especially, JP-A-9-108601 discloses an oil-holding portion constituted by a porous cylindrical molded product. The porous cylindrical molded includes heat-resisting fibers bound together by a binder and fine communicating voids in the absence of the binder between the fibers. A group of pores is uniformly distributed in a pore size range of from 0.05 to 2 mm and has a total void percentage of from 30 to 90% The oil application roller using the porous cylindrical molded product is convenient in that the oil-holding member can hold a large amount of silicone oil and in that the large amount of silicone oil can be used for stable oil application over a long term.
When the oil application roller is used in a fixing apparatus in a color copying machine or color printer, there is, however, a tendency that the amount of application of oil becomes excessive for a time when the number of sheets passes through the copying machine or printer is from hundreds of sheets to thousands of sheets after the beginning of use because oil having a relatively low viscosity of from 50 to 100 cSt is used under the necessity of applying a great amount of oil onto the fixing roll compared with a monochromatic copying machine or monochromatic printer. For the same reason, the amount of leaking oil increases also while machine is stopped. There is still a problem that an excessive amount of silicone oil is applied onto the fixing roll for a short time just after the re-start of the paper-passing operation.
Further, when copying or printing is made on plastic sheets of OHP sheet, fixation of toner is affected even by slight irregularity of application of oil so that density irregularity is apt to occur in a fixed image easily. Particularly in the case of the oil migration layer formed by winding tape-like felt spirally without any gap, there is a slight bump in an abutting portion between end surfaces of the tape-like felt though the surface of the oil migration layer looks flat. Because the bump is extended spirally, the bump causes stripe-like irregularity of application of oil and, accordingly, causes density irregularity of a fixed image.
In order to solve this problem, there is a method in which an elastic layer is further provided between the oil application amount control layer and the oil migration layer so that a buffering function based on the elastic deformability of the elastic layer prevents a phenomenon that contact pressure between the oil application roller and the fixing roller is changed by the unevenness of the felt layer as the oil migration layer to thereby cause the aforementioned irregularity of application of oil and irregularity of fixing of an image. The method is, however, complex in production because of the necessity of forming the two layers, that is, the felt layer formed by spirally winding tape-like felt and the elastic layer. Hence, there is a problem that the production cost increases.
Further, in the background-art oil application roller, for example, having an oil migration layer or an elastic layer provided to a cylindrical or pad-like molded product, and an oil application amount control layer further bonded thereto, the oil application amount control layer is displaced or peeled because of shortage of adhesive strength due to the small adhesive area. Hence, there is a further problem that it is difficult to apply release oil on the fixing roll continuously and stably.
In view of the foregoing, an object of the present invention is to provide an oil application apparatus which has such a simple structure as to be produced easily, which can apply a proper amount of low-viscosity silicone oil just after the beginning of use while the amount of wasteful leaking oil during use is so small that there is no risk of application of excessive oil just after the re-start of the paper-passing operation and which can perform such uniform oil application that density irregularity does not occur in a fixed image even in the case where a subject of copying or printing is OHP sheets.
Another object of the present invention is to provide an oil application apparatus in which an oil application amount control layer is not displaced or peeled when the apparatus operates and in which the oil application amount control layer can be bonded to an oil-holding member easily.
Upon such circumstances, the inventors of the present invention have made examination eagerly. As a result, it has been found that, when the oil migration layer provided between the porous oil-holding member and the oil application amount control layer is constituted by one or two layers of heat-resisting fiber felt having a specific bending resistance, there is no necessity of providing two different kinds of felt-like materials or an elastic layer as a measure against irregularity of application of oil and irregularity of density of a fixed image so that a simple structure to be produced easily can be provided to thereby make it possible to reduce cost and make it possible to perform very uniform oil application without density irregularity of the fixed image even in the case where a subject of copying or printing is OHP paper. Hence, the present invention has been accomplished.
That is, the present invention provides an oil application apparatus characterized in that a porous oil-holding member is impregnated with silicone oil, and heat-resisting fiber felt having a bending resistance in the range of 30 to 90 mm is provided on an oil application side of the porous oil-holding member, and an oil application amount control layer is further provided on the oil application side of the heat-resisting fiber felt.